The role of rhodium in the mechanism of the water–gas shift over zirconia supported iron oxide

A study is carried out to analyze the activity contribution of the redox and associative mechanism in the water–gas shift (WGS) over a new catalyst system (Rh/Fe2O3/ZrO2). The catalyst performance was evaluated at low H2O/CO ratio (∼2) in the temperature range of 623–773 K at 1 bar and 21 bar, and space velocities relevant for industrial applications, and complemented by kinetic measurements at 21 bar, and physico-chemical characterization techniques. In zirconia supported iron oxide (Fe2O3/ZrO2), the redox mechanism is considered to be operational and over zirconia supported rhodium associative mechanism is dominant. Rhodium in Rh/Fe2O3/ZrO2 enhances the WGS activity by promoting the redox mechanism in iron oxide and also contributes to its activity through associative mechanism over rhodium particles. Small amounts of methane are produced as a side product due to the presence of rhodium. The WGS activity is inhibited by CO2 in the presence of rhodium in Rh/Fe2O3/ZrO2 and similarly as over Rh/ZrO2. Methane formation is suppressed by H2O over Rh/ZrO2 and Rh/Fe2O3/ZrO2, while CO inhibition in the methane formation is observed only over Rh/ZrO2 and not over Rh/Fe2O3/ZrO2.